The use of catalysts in the processing of hydrocarbons is well known. Catalysts enable hydrocarbon processing reactions, such as hydrotreating, hydrocracking, steam cracking or upgrading reactions, to proceed more efficiently under various reaction conditions with the result that the overall efficiency and economics of a process are enhanced. Different catalysts are more effective in certain reactions than others and, as a result, significant research is conducted into the design of catalysts in order to continue to improve the efficiencies of reactions. Many factors such as catalyst chemistry, particle size, support structure and the reaction chemistry to produce the catalyst are very important in determining the reaction efficiency and effectiveness as well as the economics of a particular catalyst.
Catalysts can be generally categorized in one of two classes, namely supported and unsupported catalysts. Supported catalysts are more widely used due to several advantages including the high surface area available to anchor active phases (usually metals) predominantly responsible for the catalytic activity on the support. Supported catalysts may also be advantaged over unsupported catalysts as no separation of catalysts from reactants is required from within or outside the reaction vessel.
While effective in many applications, supported catalysts can be disadvantaged when performing under conditions and with feedstocks that inevitably produce solid deposits within the porous network of the catalyst support. In such cases a progressive loss of catalyst performance due to pore plugging occurs, making larger quantities of catalysts required for a given process to ensure that the reactions progress efficiently.
Unsupported catalysts are not physically supported on a solid matrix; they may be less expensive to produce as no solid support matrix is required. In reactions where unsupported catalysts are soluble in the reaction media, they may be disadvantaged by the difficulties of recovering them from the products stream which will increase reaction or production costs as catalysts must be replaced or, alternatively requires that the reactants are subjected to costly separation processes. Frequently, unsupported metal based catalysts with equivalent particle size or diameter than supported catalysts offer lower surface area of catalytic active phases. However, unsupported catalysts with particle size below the micron range are advantaged over supported catalysts by increasing the surface area available of active sites for reaction and thus, may enable a reaction to proceed more efficiently as compared to a reaction utilizing a supported catalyst.
While there is no universal rule with respect to the superiority of one class of catalyst over another, in many systems, a primary consideration in choosing or designing a catalyst system is the potential trade-off between the reaction efficiency and costs of unsupported catalysts versus supported catalysts.
As a result, there is a continued need for catalyst compositions for use in certain reactions wherein the reaction efficiencies of unsupported catalysts are combined with the cost efficiencies of supported catalysts.
Furthermore, there has been a need for catalyst compositions in the micro to nanometer size to enhance surface area efficiencies. Ideally, catalyst compositions in this size range should be produced from relatively simple chemistry so as to minimize production costs. It is also an advantage if such unsupported catalyst compositions can be readily separated from the reaction process so as to enable effective recovery and recycling of the catalyst back to the reaction process.